The Institute of Chronobiology was established in 1982 to promote research in human biological rhythms and to apply findings to clinical problems related to sleep and behavior. Chronobiology has special importance for understanding behavioral aspects of aging and disorders of affect. The objectives of the Chronobiology Core/Laboratory of the CRC/GAD will be to: 1) Function as a resource to investigators by providing a broad range of physiological variables in both laboratory-based and ambulatory studies of elderly depressives; 2) consult with and develop joint research with other investigators of the Developing CRC; 3) train new investigators; and 4) initiate two new pilot studies that exemplify the chronobiological approach to geriatric depressive disorders. Study #1 will examine the combined effects of aging and depression on the circadian secretory pattern of plasma melatonin. As a marker of the circadian timing system, melatonin secretion is not sensitive to "masking" effects of sleep, making it possible to conduct short, definitive chronobiological studies of depression. In addition, aging and depression have each been associated with impaired melatonin secretion; if the effects are additive, melatonin secretion may be a sensitive biological marker of geriatric depression. The relationship of melatonin secretion to severity of depression will be examined in detail, its status as a marker of the depressive state will be tested by comparing melatonin levels before and after pharmacological treatment of depression, and the possibility that it may be a trait marker of depression will be examined by relating melatonin levels during remission of depression to its relapse/recurrence. Study #2 will examine the effects of a different treatment, electroconvulsive therapy (ECT), on the circadian timing systems of geriatric depressives. Using the well-established circadian variable of body core temperature, two aspects of ECT will be studied. First, we will determine the extent to which ECT alters the circadian timing system of geriatric patients. Second, a partial phase response curve to ECT will be established in order to examine the degree to which the circadian timing system may play a role, both mechanistically and as a predictive index, in the acute and long-term outcome of electroconvulsive therapy. In addition, it will be possible, during the baseline phase of the study, to evaluate putative differences in the circadian systems of elderly depressed patients relative to healthy elderly subjects. In conducting these studies, the Chronobiology Core/Laboratory will thus serve as the initial user of its own resources. As the studies generate, data and interest on the part of trainees and potential collaborators, independent external funding will be sought, both to complete the studies and to pursue new leads generated by the findings.